Low NMP aqueous polyurethane composition

ABSTRACT

An aqueous composition with a sediment content ≦5%, comprising a polyurethane dispersion wherein the polyurethane has an acid value in the range of from 25 to 65 mgKOH/g and comprises (i) 36 to 60 wt % of at least one aromatic polyisocyanate and where the polyurethane is prepared in the presence of (a) ≦5 wt % of 1-methyl-2-pyrrolidinone by weight of the polyurethane, (b) 5 to 100 wt % of 1-ethyl-2-pyrrolidinone by weight of polyurethane and (c) water.

This application is the US national phase of international applicationPCT/EP2005/006934 filed 28 Jun. 2005 which designated the U.S. andclaims benefit of GB 0414598.3, dated 30 Jun. 2004, the entire contentof which is hereby incorporated by reference.

The present invention relates to an aqueous composition comprising apolyurethane dispersion, an aqueous composition comprising apolyurethane vinyl hybrid dispersion, a process for making the aqueouscompositions and the use of such aqueous compositions in coatings, suchas coatings for floors.

It is well known in the coatings industry that polyurethane dispersionscan be applied to a variety of substrates to provide coatings with goodresistance to abrasion, good chemical resistance, good flexibility anddurability as well as having good adhesion to the substrate. A majorapplication for such coatings is as clear coatings for wood flooring.

Conventionally polyurethane compositions are prepared in organicsolvents which evaporate on drying after application to a substrate. Forreasons of environmental protection and adherence to solvent emissionguidelines water-based polyurethane dispersions and polyurethane vinylhybrid dispersions have been developed and are well known.

It is also known that polyurethanes based predominantly on aromaticpolyisocyanates have better hardness, better resistance againstchemicals and better mechanical properties in for example flooringapplications than polyurethanes based predominantly on aliphaticisocyanates. Furthermore the use of aromatic polyisocyanates tends to bemore cost effective than the use of aliphatic polyisocyanates.

U.S. Pat. No. 4,801,644 and U.S. Pat. No. 4,927,876 disclose thepreparation of aqueous polyurethane compositions containingdiphenylmethane-2,4-diisocyanate utilising 1-methyl-2-pyrrolidinone asan organic solvent.

U.S. Pat. No. 5,173,526 discloses a method for making aqueouspolyurethane-vinyl polymer dispersions with 1-methyl-2-pyrrolidinonebeing used as a solvent.

U.S. Pat. No. 5,314,942 discloses an aqueous polymer dispersioncontaining a vinyl polymer prepared in-situ and a water-dispersiblepolyurethane having pendent polyethylene oxide chains and utilising1-methyl-2-pyrrolidinone.

U.S. Pat. No. 6,239,209 discloses an air-curable polyurethane-acrylichybrid interpenetrating polymer network.

U.S. Pat. No. 6,566,438 discloses aliphatic polyurethane vinyl hybridcompositions containing 1-methyl-2-pyrrolidinone.

JP 06-08553 and JP 03-193446 disclose the preparation ofpolyurethane-polyurea dispersions.

However such water-based polyurethanes and polyurethane vinyl hybrids,especially if based on aromatic polyisocyanates, still utilisesignificant amounts of 1-methyl-2-pyrrolidinone (NMP) to reduce theviscosity during production, which remains in the aqueous compositionafter dispersion of the polyurethane in water and then evaporates ondrying.

Proposed changes in future legislation from irritant to toxic on thelabelling of products containing NMP are resulting in increased effortsto minimise and even eliminate the use of NMP altogether. Thereforethere is a need for a replacement diluent for NMP which has a moreacceptable toxicological profile.

A disadvantage resulting from the preparation of polyurethanes based onaromatic isocyanates and with very low NMP levels or with no NMP at allis that the processing usually results in a high level of sedimentand/or gel.

U.S. Pat. No. 4,318,833 discloses water-reducible acrylic-urethanecoating compositions where the polyurethanes are prepared in a solventmixture.

U.S. Pat. No. 4,644,030 discloses aqueous polyurethane-polyolefincompositions.

U.S. Pat. No. 5,137,961 discloses the preparation of a surfactant freeaqueous polymer dispersion containing an anionic polyurethane basedsubstantially on aliphatic isocyanates and a vinyl polymer where vinylmonomers are used to reduce the viscosity of the reaction mixture.

U.S. Pat. No. 6,635,706 discloses a pre-crosslinked urethane-acrylicdispersion.

U.S. Pat. No. 6,635,723 discloses a process for making a solvent-freepolyurethane dispersion using a relatively low aliphatic polyisocyanatecontent.

U.S. Pat. No. 6,720,385 discloses aqueous polyurethane latexes preparedwithout the use of organic solvents using relatively high levels ofpolyethylene oxide polyols.

JP 09-150568, JP 09-150569, JP 09-102861 and JP 09-038674 disclose thepreparation of aqueous polyurethane compositions utilizing unsaturatedmonomers and hydroxyl groups bearing organic solvents.

U.S. Pat. No. 3,705,164, U.S. Pat. No. 4,066,591, U.S. Pat. No.6,538,046, U.S. Pat. No. 5,662,966 and U.S. Pat. No. 5,637,639 all teachthe preparation of polyurethane by making a prepolymer in solvent suchas acetone followed by dispersion in water, chain extension of theprepolymer and removal of the solvent. Removal of solvent tends to belaborious and costly and there is also an associated risk of fire.

Furthermore in the prior art there is a desire to keep the level ofpolyisocyanate used in the polyurethane preparation to a minimum inorder to get acceptable processing.

Therefore, in compositions with a high aromatic isocyanate content and alow NCO/OH ratio (which result in relatively high molecular weightisocyanate-terminated prepolymers with a high viscosity and which aredifficult to process) it is necessary to use a suitable diluent tocontrol viscosity and to facilitate the dispersing process. The problemto solve is to replace NMP with a toxicologically more acceptablesolvent during the synthesis of polyurethanes with a high aromaticisocyanate content, while maintaining the good processing and finalproperties that can be obtained when using NMP.

A suitable diluent should comply with a number of requirements. Sincethe diluent will be used in the isocyanate-terminated prepolymerpreparation, it should not contain any isocyanate-reactive groups. Sincethe diluent will also be present during any chain extension withdiamines and hydrazine compounds, the diluent should also not bereactive with commonly used chain extenders such as ethylene diamine andhydrazine.

Dimethylolpropionic acid (DMPA) is the most commonly used acidfunctional diol to incorporate water dispersibility into thepolyurethane and therefore the diluent should also be a good solvent forDMPA. Preferably it should be possible to prepare a 30 wt % solution ofDMPA in this diluent. Furthermore to promote a good water dispersibilityof the isocyanate-terminated prepolymer, the diluent should be misciblewith water.

The viscosity of the diluent at 25° C. should be <6 mPas and morepreferably <4 mPas, in order to have a good diluting effect.

For handling purposes (such as transport and storage) in any weatherconditions, the diluent should have a freezing point <−20° C.

To support film formation after application of the composition to asubstrate the diluent should preferably have a boiling point >160° C.and more preferably >200° C. If a diluent with a lower boiling point isused the diluent may evaporate from the film before sufficient filmformation has taken place, thus leading to a reduced level of chemicaland water resistance. Within a typical production environment, onlydiluents with a minimal flashpoint are usually allowable. The preferredflash point of the diluent is >75° C., more preferably >85° C.

Alternatives to NMP have been reviewed in the art, for exampledimethylformamide can be used, however dimethylformamide has anunfavourable toxicological profile and a low flash point. Dimethylacetamide and diethylene glycol dimethyl ether have an unacceptabletoxicological profile. Tetramethylurea has a melting point of −1° C.which can cause problems in cold conditions. Dimethylsulphoxide also hasan unacceptably high melting point of 18.5° C. and has an unsuitablegarlic odour. Sulpholane has a melting point of 27.5° C. which wouldrequire heating of the solvent before use and also has a strong odourdue to impurities. Aromatic diluents such as toluene and xylene mayhamper water dispersibility of the polyurethane due to their poormiscibility with water. Polyurethane dispersions prepared withbutyrolactone appear to be instable and the lactone group is also ableto react with chain extenders such as hydrazine and ethylene diamine.Methylethylketone has a flashpoint of −4° C. and a strong odour.

We have now found that it is possible to prepare polyurethanes with ahigh level of aromatic polyisocyanate content as well as a low NMPcontent and polyurethane vinyl hybrids with a low NMP content and yetmaintain good processability with low levels of sediment to givedispersions that may form hard and resistant coatings using1-ethyl-2-pyrrolidinone as a diluent.

According to the present invention there is provided an aqueouscomposition with a sediment content ≦5%, comprising a polyurethanedispersion and containing ≦5 wt % of 1-methyl-2-pyrrolidinone by weightof the polyurethane, wherein the polyurethane has an acid value in therange of from 24 to 65 mgKOH/g and is obtained by the reaction of:

A) an isocyanate-terminated prepolymer formed from componentscomprising:

-   -   (i) 30 to 60 wt % of at least one aromatic polyisocyanate;    -   (ii) 0 to 30 wt % of at least one aliphatic polyisocyanate;    -   (iii) 0 to 15 wt % of at least one isocyanate-reactive polyol        bearing ionic and/or potentially ionic water-dispersing groups        with a weight average molecular weight ≦500 g/mol;    -   (iv) 0 to 10 wt % of at least one isocyanate-reactive polyol        bearing non-ionic water-dispersing groups;    -   (v) 0 to 15 wt % of at least one isocyanate-reactive polyol with        a weight average molecular weight ≦500 g/mol not comprised        by (iii) or (iv);    -   (vi) 20 to 58 wt % of at least one isocyanate-reactive polyol        not comprised by (iii), (iv) or (v);    -   where (i)+(ii)+(iii)+(iv)+(v)+(vi) add up to 100 wt %;    -   where the NCO/OH ratio is in the range of from 1.2:1 to 2.5:1;        and

B) at least one active-hydrogen chain extending compound;

where the active hydrogen/NCO ratio is in the range of from 0.4:1 to1.3:1; in the presence of (a) ≦5 wt % of 1-methyl-2-pyrrolidinone byweight of polyurethane, (b) 5 to 100 wt % of 1-ethyl-2-pyrrolidinone byweight of polyurethane and (c) water.

Preferably the aqueous composition comprising a polyurethane dispersioncontains ≦3 wt %, more preferably ≦1 wt % and most preferably 0 wt % ofNMP by weight of the polyurethane.

For clarity by weight of polyurethane is meant the weight ofpolyurethane solids.

According to a second embodiment of the present invention there isprovided an aqueous composition with a sediment content ≦5%, comprisinga polyurethane vinyl hybrid dispersion and containing ≦0.5 wt % of1-methyl-2-pyrrolidinone by weight of the composition;

wherein the polyurethane has an acid value in the range of from 24 to 65mgKOH/g and is obtained by the reaction of:

A) an isocyanate-terminated prepolymer formed from componentscomprising:

-   -   (i) 30 to 60 wt % of at least one aromatic polyisocyanate;    -   (ii) 0 to 30 wt % of at least one aliphatic polyisocyanate;    -   (iii) 0 to 15 wt % of at least one isocyanate-reactive polyol        bearing ionic and/or potentially ionic water-dispersing groups        with a weight average molecular weight ≦500 g/mol;    -   (iv) 0 to 10 wt % of at least one isocyanate-reactive polyol        bearing non-ionic water-dispersing groups;    -   (v) 0 to 15 wt % of at least one isocyanate-reactive polyol with        a weight average molecular weight ≦500 g/mol not comprised        by (iii) or (iv);    -   (vi) 20 to 58 wt % of at least one isocyanate-reactive polyol        not comprised by (iii), (iv) or (v);    -   where (i)+(ii)+(iii)+(iv)+(v)+(vi) add up to 100 wt %;    -   where the NCO/OH ratio is in the range of from 1.2:1 to 2.5:1;        and

B) at least one active-hydrogen chain extending compound;

where the active hydrogen/NCO ratio is in the range of from 0.4:1 to1.3:1; in the presence of (a) ≦5 wt % of 1-methyl-2-pyrrolidinone byweight of polyurethane, (b) 5 to 100 wt % of 1-ethyl-2-pyrrolidinone byweight of polyurethane and (c) water.

Preferably components (i)+(ii)+(iii)+(v) add up to ≧42 wt %, morepreferably ≧50 wt % and especially ≧55 wt %.

1-Ethyl-2-pyrrolidinone (NEP) is added as a diluent before and/or duringand/or after the isocyanate-terminated prepolymer formation to controlthe viscosity. Preferably the NEP is present during the formation of theisocyanate-terminated prepolymer.

Preferably 10 to 60 wt % and more preferably 10 to 35 wt % of1-ethyl-2-pyrrolidinone by weight of polyurethane is used.

By a polyurethane vinyl hybrid is meant that a vinyl polymer is preparedby the polymerisation of unsaturated vinyl monomers in the presence ofthe polyurethane. The vinyl polymer may be grafted to the polyurethaneor alternatively the vinyl polymer is not grafted to the polyurethaneduring the polymerisation.

Preferably the ratio of polyurethane to vinyl polymer in thepolyurethane vinyl hybrid is in the range of from 95:5 to 30:70, morepreferably 85:15 to 35:65 and most preferably 75:25 to 40:60.

Preferably the acid value of the polyurethane is in the range of from 25to 55 mgKOH/g and more preferably 25 to 45 mgKOH/g of polyurethane.

For clarity the terms polyurethane, vinyl polymer, vinyl monomer andpolyurethane vinyl hybrid are intended to cover the singular as well asthe plural.

The aromatic polyisocyanate component (i) can be a mixture of organicpolyisocyanates. This term (for the sake of clarity) being intended tomean compounds in which all of the isocyanate groups are directly bondedto an aromatic group, irrespective of whether aliphatic groups are alsopresent. Examples of suitable aromatic polyisocyanates include but arenot limited to p-xylylene diisocyanate, 1,4-phenylene diisocyanate,2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 4,4′-methylenebis(phenyl isocyanate), polymethylene polyphenyl polyisocyanates,2,4′-methylene bis(phenyl isocyanate) and 1,5-naphthylene diisocyanate.

Preferably the isocyanate-terminated prepolymer comprises 30 to 60 wt %,more preferably 30 to 55 wt %, most preferably 30 to 55 wt % andespecially 36 to 55 wt % of component (i).

Preferably component (i) comprises methylene bis(phenyl isocyanate) (allisomers) and/or toluene diisocyanate (all isomers). More preferablycomponent (i) comprises 10 to 70 wt % of toluene diisocyanate and from90 to 30 wt % of methylene bis(phenyl isocyanate). Even more preferablycomponent (i) comprises from 25 to 60 wt % of toluene diisocyanate andfrom 75 to 40 wt % of methylene bis(phenyl isocyanate) where preferablythe methylene bis(phenyl isocyanate) is a mixture of 4,4′- and2,4′-methylene bis(phenyl isocyanate) where preferably the mixturecontains from 5 to 70 wt % of 2,4′-methylene bis(phenyl isocyanate).

The aliphatic polyisocyanate component (ii) can be a mixture ofaliphatic isocyanates. This term (for the sake of clarity) beingintended to mean compounds in which all of the isocyanate groups aredirectly bonded to aliphatic or cycloaliphatic groups, irrespective ofwhether aromatic groups are also present.

Examples include but are not limited to ethylene diisocyanate,para-tetra methylxylene diisocyanate (p-TMXDI), meta-tetra methylxylenediisocyanate (m-TMXDI), 1,6-hexamethylene diisocyanate, isophoronediisocyanate, cyclohexane-1,4-diisocyanate, and 4,4′-dicyclohexylmethanediisocyanate. Preferably component (ii) comprises isophoronediisocyanate and 4,4′-dicyclohexylmethane diisocyanate.

Preferably the isocyanate-terminated prepolymer comprises 0 to 12 wt %,more preferably 0 wt % of component (ii).

Preferably at least 70 wt %, more preferably at least 85 wt % and mostpreferably at least 95 wt % of the polyisocyanates in components (i) and(ii) have two isocyanate groups.

Aromatic or aliphatic polyisocyanates which have been modified by theintroduction of urethane, allophanate, urea, biuret, uretonimine,urethdione or isocyanurate residues can be used for components (i) and(ii) respectively.

The isocyanate-reactive components (iii) to (vi) will normally consistof a polyol component bearing isocyanate-reactive groups which may alsobear other reactive groups. By a polyol component it is also meant toinclude compounds with one or more isocyanate-reactive groups such as—OH, —SH, —NH— and —NH₂.

Water-dispersing groups are preferably introduced by employing at leastone isocyanate-reactive compound (or less preferably anisocyanate-functional compound) bearing a non-ionic and/or ionicwater-dispersing groups as a component in the preparation of theisocyanate-terminated prepolymer. Preferably component (iii) comprisesanionic or potentially anionic water-dispersing groups. Examples ofcompounds bearing anionic water-dispersing groups include phosphoricacid groups, sulphonic acid groups and/or carboxylic acid groups such ascarboxyl group containing diols and triols. Preferably component (iii)comprises dihydroxy alkanoic acids such as 2,2-dimethylolpropionic acid(DMPA) and/or 2,2-dimethylolbutanoic acid (DMBA).

The anionic water-dispersing groups are preferably fully or partially inthe form of a salt. Conversion of for example a potentially anionicwater-dispersing group to the salt form (i.e. anionic water-dispersinggroup) may be effected by neutralisation with a base, preferably duringthe preparation of the aqueous composition of the present invention.

If the anionic water-dispersing groups are neutralised, the base used toneutralise the groups may be selected from ammonia, an amine, aninorganic base and combinations thereof. Preferably ammonia andinorganic bases are only used in combination with other neutralisingagents, where generally less than 0.5 equivalent, more preferably lessthan 0.2 equivalent of ammonia and/or inorganic base per carboxylic acidgroup is used. Tertiary amines are preferred. Tertiary amines includefor example triethylamine, dimethyl amino ethyl methacrylate or oxygencontaining amines. Preferably ≧60 wt %, more preferably ≧80 wt % andespecially 100 wt % of the polyurethane is neutralised with an oxygencontaining amine.

Preferably the oxygen containing amine is selected from the groupconsisting of N-ethyl morpholine; N-methyl morpholine; and R¹(R²)NR³OHwith a Mn in the range of from 88 to 118, where R, R₂ and R₃ are eachindependently C₁ to C₄-alkyl (for example dimethyl isopropanol amine);and more preferably the oxygen containing amine isN,N-dimethylethanolamine. Suitable inorganic bases include alkalihydroxides and carbonates, for example lithium hydroxide, sodiumhydroxide or potassium hydroxide. A quaternary ammonium hydroxide, forexample N⁺(CH₃)₄(OH), can also be used. Generally a base is used whichgives counter ions that may be desired for the composition. For example,preferred counter ions include Li⁺, Na⁺, K⁺, NH₄ ⁺ and substitutedammonium salts. When inorganic bases are used they are preferably usedin combination with at least one tertiary amine as described above.

Neutralisation is usually based on the equivalent of ionic groups, andpreferably the ionic water-dispersing groups in theisocyanate-terminated prepolymer are neutralised with a neutralisingagent in the range of from 0.5:1 to 1.4:1, more preferably 0.6:1 to1.4:1, most preferably 0.75:1 to 1.30:1 and especially 0.95:1 to 1.25:1.At lower levels not enough of the prepolymer is dispersed leading to anincrease in sediment levels and at higher levels an increase in pH mayoccur, resulting in more isocyanate groups reacting with water. Thisresults in an increase in foam and a reduction in the molecular weightof the polyurethane. Additionally at higher levels a discoloration ofthe resultant coating or substrate may occur especially when applied tocertain types of wood such as oak.

Cationic water-dispersible groups can also be used, but are lesspreferred. Examples include pyridine groups, imidazole groups and/orquaternary ammonium groups which may be neutralised or permanentlyionised (for example with dimethylsulphate).

Preferably the isocyanate-terminated prepolymer comprises 5.0 to 12.0 wt% and more preferably 6.0 to 10.0 wt % of component (iii).

Component (iv) bears non-ionic water-dispersing groups. Preferrednon-ionic water-dispersing groups are polyalkylene oxide groups whereethylene oxide is the major component. A small part of the polyethyleneoxide segments can be replaced by propylene oxide segments and/orbutylene oxide segments, however the polyalkylene oxide group shouldstill contain ethylene oxide as a major component. Most preferably thenon-ionic water-dispersing group comprises at least 90 wt %, morepreferably at least 95 wt %, especially at least 98 wt % and mostespecially 100 wt % of ethylene oxide. When the water-dispersible groupis polyethylene oxide, preferably the polyethylene oxide group has amolecular weight from 175 to 5000 Daltons, more preferably from 350 to2200 Daltons, most preferably from 660 to 1600 Daltons.

Examples of preferred compounds bearing non-ionic water-dispersinggroups include methoxy polyethylene glycol (MPEG) with molecular weightsof for example 350, 550, 750, 1000 and 2000, as described in EP 0317258.

An excess of isocyanate-reactive polyols bearing non-ionicwater-dispersing groups may result in lower König Hardness and lowerchemical or stain resistance of the resultant coating. Preferably theisocyanate-terminated prepolymer comprises 0 to 7 wt %, more preferably0 wt % of component (iv).

Examples of component (v) include but are not limited to ethyleneglycol, neopentyl glycol and 1,4-cyclohexyldimethanol and lesspreferably water. Also included are low molecular weight polyesterpolyols which include hydroxyl-terminated reaction products ofpolyhydric alcohols such as ethylene glycol, propylene glycol,diethylene glycol, neopentyl glycol, 1,4-butanediol, 1,6-hexanediol,furan dimethanol, cyclohexane dimethanol, glycerol, trimethylolpropaneor mixtures thereof, with polycarboxylic acids, especially dicarboxylicacids or their ester-forming derivatives, for examples succinic,glutaric and adipic acids or their methyl esters, phthalic anhydrides ordimethyl terephthalate. Polyesters obtained by the polymerisation oflactones, for example caprolactone in conjunction with a polyol may alsobe used.

Preferably component (v) has an average of 1.8 to 2.5isocyanate-reactive groups and more preferably component (v) has twohydroxy functional groups.

Preferably the weight average molecular weight of component (v) is inthe range of from 62 to 300 and more preferably 84 to 200 g/mol.

Preferably the isocyanate terminated prepolymer comprises 2 to 8 wt %and more preferably 3 to 6 wt % of component (v).

Examples of component (vi) include but are not limited to highermolecular weight examples of the compounds listed for component (v) suchas polyesters, polyether polyols polyesteramides, polythioethers,polycarbonates, polyacetals, polyolefins and polysiloxanes.

Polyesteramides may be obtained by the inclusion of amino-alcohols suchas ethanolamine in polyesterification mixtures. Polyesters whichincorporate carboxy groups may be used, for example polyesters whereDMPA and/or DMBA is used during the synthesis, provided that theesterification is carried out under conditions which allow the retentionof the carboxy functionality in the final polyester.

A feature of such carboxy functional polyesters is that they cancontribute to the dispersibility of the isocyanate-terminated prepolymerin water, thus allowing a lower level of component (iii) to be used.

Polyether polyols which may be used include products obtained by thepolymerisation of a cyclic oxide, for example ethylene oxide, propyleneoxide or tetrahydrofuran or by the addition of one or more such oxidesto polyfunctional initiators, for example water, methylene glycol,ethylene glycol, propylene glycol, diethylene glycol, cyclohexanedimethanol, glycerol, trimethylopropane, pentaerythritol or Bisphenol A.Especially useful polyether polyols include polyoxypropylene diols andtriols, poly (oxyethylene-oxypropylene) diols and triols obtained by thesimultaneous or sequential addition of ethylene and propylene oxides toappropriate initiators and polytetramethylene ether glycols obtained bythe polymerisation of tetrahydrofuran. Particular preferred arepolyester diols.

Components (v) and (vi) may also include crosslinking groups.Crosslinking groups are well known in the art and include groups whichmay crosslink at ambient temperature (20±3° C.) by a number ofmechanisms including but not limited to autoxidation (for example byfatty acid groups containing unsaturated bonds); Schiff basecrosslinking (for example the reaction of carbonyl functional groupswith carbonyl reactive amine and/or hydrazine functional groups); silanecrosslinking (for example the reaction of alkoxy silane groups in thepresence of water) and epoxy groups crosslinking with epoxy-reactivefunctional groups.

When an isocyanate-terminated prepolymer is prepared, it isconventionally formed by reacting a stoichiometric excess of the organicpolyisocyanate (components (i) and (ii)) with the isocyanate-reactivecompounds (components (iii), (iv), (v) and (vi)) under substantiallyanhydrous conditions at a temperature between about 30° C. and about130° C. until reaction between the isocyanate groups and theisocyanate-reactive groups is substantially complete; preferably thereactants for the prepolymer are generally used in proportionscorresponding to a ratio of isocyanate groups to isocyanate-reactivegroups of from about 1.4:1 to about 2.0:1 and more preferably from about1.45:1 to 1.75:1.

Preferably the practical NCO % of the prepolymer at the end ofprepolymer preparation should be equal to or less than the theoreticalNCO %. If the practical NCO % is greater than the theoretical NCO %,then the prepolymer reaction has not been completed which will affectthe reproducibility of the dispersion ability since the amount ofresidual free polyols and/or isocyanates may vary. Additionally, if theprepolymer reaction has not been completed and dispersion is started thedispersability will be decreased as any unreacted polyols and freeisocyanates reduce the water up take and will therefore result in moresediment.

If desired, catalysts such as dibutyltin dilaurate and stannous octoate,zirconium or titanium based catalysts may be used to assist thepolyurethane formation. Preferably no catalyst is used.

Active hydrogen-containing chain extending compounds, which may bereacted with the isocyanate-terminated prepolymer includeamino-alcohols, primary or secondary diamines or polyamines, hydrazineand substituted hydrazines.

Examples of such chain extending compounds useful herein includealkylene diamines such as ethylene diamine and cyclic amines such asisophorone diamine. Also compounds such as hydrazine, azines such asacetone azine, substituted hydrazines such as, for example, dimethylhydrazine, 1,6-hexamethylene-bis-hydrazine, carbodihydrazine, hydrazidesof dicarboxylic acids and sulphonic acids such as adipic aciddihydrazide, oxalic acid dihydrazide, isophthalic acid dihydrazide,hydrazides made by reacting lactones with hydrazine, bis-semi-carbazide,and bis-hydrazide carbonic esters of glycols may be useful. Water itselfmay be effective as an indirect chain extending compound. Anothersuitable class of chain extending compounds are the so-called“Jeffamine” compounds with a functionality of 2 or 3 (available fromHuntsman). These are PPO or PEO-based di or triamines, e.g. “Jeffamine”T403 and “Jeffamine” D-400.

Preferably the amount of active-hydrogen chain extending compound otherthan water to isocyanate (NCO) groups is in the range of from 0.5:1 to1.2:1, more preferably 0.6:1 to 1.1:1, especially 0.75:1 to 1.02:1 andmost preferably 0.78:1 to 0.98:1.

Where the chain extender is other than water, for example a polyamine orhydrazine, it may be added to an aqueous dispersion of theisocyanate-terminated prepolymer or preferably, it may already bepresent in the aqueous medium when the isocyanate-terminated prepolymeris dispersed therein.

The isocyanate-terminated prepolymer may be dispersed in water usingtechniques well known in the art.

Preferably, the isocyanate-terminated prepolymer is added to the waterwith agitation or, alternatively, water may be stirred into theisocyanate-terminated prepolymer.

Vinyl monomers as described below may also be added to the aqueous phasebefore and/or during and/or after dispersing the isocyanate-terminatedprepolymer in water. The function of these vinyl monomers is notprimarily as a diluent to control the viscosity of theisocyanate-terminated prepolymer formation but to contribute to thein-situ preparation of a vinyl polymer although they may of courseinherently contribute to the overall viscosity.

All of the vinyl monomer may be present before commencement ofpolymerisation, or the vinyl monomer may be added to the reaction mediumduring the course of the polymerisation (in one or more stages orcontinuously). For example, when the aqueous dispersion of theisocyanate-terminated prepolymer is formed in the process to make thepolyurethane as described above, some or all of the vinyl monomer may beadded before and/or after and/or during the isocyanate-terminatedprepolymer preparation prior to its dispersion into water or all of thevinyl monomer may be added subsequent to the dispersion (or some or allof the vinyl monomer may have already been added to the water prior tothe dispersion of the isocyanate-terminated prepolymer therein).

Examples of such vinyl monomers include but are not limited to vinylmonomers such as 1,3-butadiene, isoprene; trifluoro ethyl(meth)acrylate(TFEMA); dimethyl amino ethyl(meth)acrylate (DMAEMA); styrene, α-methylstyrene, (meth)acrylic amides and (meth)acrylonitrile; vinyl halidessuch as vinyl chloride; vinylidene halides such as vinylidene chloride;vinyl ethers; vinyl esters such as vinyl acetate, vinyl propionate,vinyl laurate; vinyl esters of versatic acid such as VeoVa 9 and VeoVa10 (VeoVa is a trademark of Resolution); heterocyclic vinyl compounds;alkyl esters of mono-olefinically unsaturated dicarboxylic acids such asdi-n-butyl maleate and di-n-butyl fumarate and in particular, esters ofacrylic acid and methacrylic acid of formula CH₂═CR¹—COOR² wherein R¹ isH or methyl and R² is optionally substituted alkyl or cycloalkyl of 1 to20 carbon atoms (more preferably 1 to 8 carbon atoms) examples of whichare methyl (meth)acrylate, ethyl(meth)acrylate, butyl(meth)acrylate (allisomers), octyl (meth)acrylate (all isomers),2-ethylhexyl(meth)acrylate, isopropyl(meth)acrylate and n-propyl(meth)acrylate. Preferred monomers of formula CH₂═CR¹—COOR² includebutyl (meth)acrylate (all isomers), methyl(meth)acrylate,octyl(meth)acrylate (all isomers) and ethyl(meth)acrylate.

The vinyl monomers may include vinyl monomers carrying functional groupssuch as crosslinker groups and/or water-dispersing groups. Suchfunctionality may be introduced directly in the vinyl polymer byfree-radical polymerisation, or alternatively the functional group maybe introduced by a reaction of a reactive vinyl monomer, which issubsequently reacted with a reactive compound carrying the desiredfunctional group.

Vinyl monomers providing ionic or potentially ionic water-dispersinggroups include but are not limited to (meth)acrylic acid, itaconic acid,maleic acid, citraconic acid and styrenesulphonic acid. Preferably suchvinyl monomers are not added until preparation of theisocyanate-terminated prepolymer is complete as they may react with theprepolymer components.

Preferably the level of vinyl monomers providing ionic or potentiallyionic water-dispersing groups is between 0 and 5 wt %, more preferablybetween 0 and 1 wt % and most preferably 0 wt % of the total level ofvinyl monomers used.

Preferably the resultant vinyl polymer has an acid value in the range offrom 0 to 20, more preferably 0 to 10 and especially 0 mgKOH/g.

Vinyl monomers providing non-ionic water-dispersing groups includealkoxy polyethylene glycol (meth)acrylates, preferably having a numberaverage molecular weight of from 350 to 3000. Examples of such monomerswhich are commercially available include ω-methoxypolyethyleneglycol(meth)acrylates.

Examples of suitable vinyl monomers providing crosslinking groupsinclude acrylic and methacrylic monomers having at least one freecarboxyl, hydroxyl, epoxy, acetoacetoxy or keto group, such as acrylicacid and methacrylic acid, glycidyl acrylate, glycidyl methacrylate,aceto acetoxy ethyl methacrylate, diacetone acrylamide, allylmethacrylate, tetraethylene glycol dimethacrylate and divinyl benzene.

If any vinyl monomer is added before dispersion of the prepolymer, thenpreferably the vinyl monomer added pre dispersion comprises 40 to 100 wt% of vinyl monomer selected from the group consisting ofmethyl(methyl)acrylate and ethyl(meth)acrylate.

If any vinyl monomer is added before dispersion of the prepolymer, thenpreferably the vinyl monomer added pre dispersion comprises ≦45 wt %,more preferably ≦40 wt % of styrene and styrene based vinyl monomers(such as α-methyl styrene).

Preferably the weight average molecular weight (Mw) of the resultantvinyl polymer is at least 60,000 Daltons, more preferably in the rangeof from 100,000 to 3,000,000 Daltons and most preferably in the range offrom 150,000 to 2,500,000 Daltons.

The Tg of a polymer herein stands for the glass transition temperatureand is well known to be the temperature at which a polymer changes froma glassy, brittle state to a rubbery state. Tg values of polymers may bedetermined experimentally using techniques such as Differential ScanningCalorimetry (DSC) or calculated theoretically using the well-known Foxequation where the Tg (in Kelvin) of a copolymer having “n”copolymerised comonomers is given by the weight fractions “W” and the Tgvalues of the respective homopolymers (in Kelvin) of each comonomer typeaccording to the equation“1/Tg=W ₁ /Tg ₁ +W ₂ /Tg ₂ + . . . W _(n) /Tg _(n)”.

The calculated Tg in Kelvin may be readily converted to ° C.

The calculated Tg of the resultant vinyl polymer is preferably in therange of from 5 to 120° C. and more preferably in the range of from 30to 110° C. If the resultant vinyl polymer comprises more than one stagethen preferably the Tg is the calculated Tg of the average resultantvinyl polymer and is in the range of from −20 to 120° C., morepreferably in the range of from 5 to 120° C. and most preferably 30 to110° C.

The weight average particle size, assuming a substantially sphericalparticle shape, of the particles in the polyurethane or polyurethanevinyl hybrid dispersion is preferably less than 500 nm, more preferablyin the range of from 20 to 300 nm and most preferably in the range offrom 20 to 200 nm. More preferably at least 60 wt %, more preferably atleast 75 wt % and most preferably at least 85 wt % of the particles havea particle size less than 500 nm. An disadvantage of a particle sizegreater than 500 nm is that the sediment content may be increasedresulting in unacceptable processing.

The polymerisation of the vinyl monomers may be carried out as a batch,step-wise, gradient or as a semi-continuous polymerisation process tomake a single or a multistage polymer.

Free-radical polymerisation of vinyl monomers will require the use of afree-radical-yielding initiator to initiate the vinyl polymerisation.Suitable free-radical-yielding initiators include K, Na or ammoniumpersulphate; hydrogen peroxide; percarbonates; organic peroxides, suchas acyl peroxides including benzoyl peroxide, alkyl hydroperoxides suchas t-butyl hydroperoxide (tBHPO) and cumene hydroperoxide; dialkylperoxides such as di-t-butyl peroxide; peroxy esters such as t-butylperbenzoate and the like; mixtures may also be used. The peroxycompounds are in some cases advantageously used in combination withsuitable reducing agents (redox systems) such as Na or K pyrosulphite orbisulphite, and iso-ascorbic acid. Metal compounds such as Fe.EDTA (EDTAis ethylene diamine tetracetic acid) may also be usefully employed aspart of the redox initiator system. Azo functional initiators may alsobe used. Preferred azo initiators include azobis(isobutyronitrile) and4,4′-azobis(4-cyanovaleric acid). The amount of initiator or initiatorsystem used is conventional, e.g. within the range 0.05 to 6 wt % basedon the total weight of vinyl monomers used. Preferred initiators includeazobis(isobutyronitrile) and/or 4,4′-azobis(4-cyanovaleric acid) andespecially redox couples that are active between 30° C. and 75° C. Mostpreferred initiators are redox couples that are active between 30° C.and 75° C. such as tBHPO and isoascorbic acid.

Molecular weight control may be provided by catalytic chain transferagents or may be provided by using chain transfer agents such asmercaptans and halogenated hydrocarbons, for example mercaptans such asn-dodecylmercaptan, n-octylmercaptan, t-dodecylmercaptan,mercaptoethanol, iso-octyl thioglycolate, C₂ to C₈ mercapto carboxylicacids and esters thereof; and halogenated hydrocarbons such as carbontetrabromide and bromotrichloromethane.

Combinations of conventional chain transfer agents and catalytic chaintransfer agents may also be used.

Surfactants can be utilised in order to assist in the dispersion of thepolyurethane and/or vinyl polymer in water (even if they areself-dispersible). Suitable surfactants include but are not limited toconventional anionic, cationic and/or non-ionic surfactants and mixturesthereof. Anionic and/or nonionic surfactants are preferred. The amountof surfactant used is preferably 0 to 6% by weight, more preferably 0 to3% by weight, and especially 0.1 to 2% by weight based on the weight ofthe solids in the aqueous composition of the invention.

In a third embodiment of the present invention there is provided aprocess for making an aqueous composition with a sediment content ≦5%,comprising a polyurethane dispersion and containing ≦5 wt % of1-methyl-2-pyrrolidinone by weight of the polyurethane, wherein thepolyurethane has an acid value in the range of from 24 to 65 mgKOH/g andwhere the process is carried out in steps comprising:

-   -   I: reacting in the presence of (a) ≦5 wt % of        1-methyl-2-pyrrolidinone by weight of polyurethane and (b) 5 to        100 wt % of 1-ethyl-2-pyrrolidinone by weight of polyurethane;        -   (i) 30 to 60 wt % of at least one aromatic polyisocyanate;        -   (ii) 0 to 30 wt % of at least one aliphatic polyisocyanate;        -   (iii) 0 to 15 wt % of at least one isocyanate-reactive            polyol bearing ionic and/or potentially ionic            water-dispersing groups with a weight average molecular            weight ≦500 g/mol;        -   (iv) 0 to 10 wt % of at least one isocyanate-reactive polyol            bearing non-ionic water-dispersing groups;        -   (v) 0 to 15 wt % of at least one isocyanate-reactive polyol            with a weight average molecular weight ≦500 g/mol not            comprised by (iii) or (iv);        -   (vi) 20 to 58 wt % of at least one isocyanate-reactive            polyol not comprised by (iii), (iv) or (v);        -   where (i)+(ii)+(iii)+(iv)+(v)+(vi) add up to 100 wt %;        -   where the NCO/OH ratio is in the range of from 1.2:1 to            2.5:1 to form an isocyanate-terminated prepolymer;    -   II: neutralising the isocyanate-terminated prepolymer with a        neutralising agent;    -   III: forming an aqueous dispersion of the isocyanate-terminated        prepolymer in water; and    -   IV: reacting the isocyanate-terminated prepolymer with at least        one active hydrogen chain-extending compound to form the        polyurethane; where the active hydrogen/NCO ratio is in the        range of from 0.4:1 to 1.3:1;

It is also possible to put a part of the NEP in the water beforedispersing the isocyanate-terminated prepolymer therein. Preferably ≧50wt %, more preferably ≧70 wt % and most preferably all of the NEP usedis present in the isocyanate-terminated prepolymer before dispersion inthe water.

In a fourth embodiment of the present invention there is provided aprocess for making an aqueous composition with a sediment content ≦5%,comprising a polyurethane vinyl hybrid dispersion and containing ≦0.5 wt% of 1-methyl-2-pyrrolidinone by weight of the composition, wherein thepolyurethane has an acid value in the range of from 24 to 65 mgKOH/g,and where the process is carried out in steps comprising:

-   -   I: reacting in the presence of (a) ≦5 wt % of        1-methyl-2-pyrrolidinone by weight of polyurethane and (b) 5 to        100 wt % of 1-ethyl-2-pyrrolidinone by weight of polyurethane;        -   (i) 30 to 60 wt % of at least one aromatic polyisocyanate;        -   (ii) 0 to 30 wt % of at least one aliphatic polyisocyanate;        -   (iii) 0 to 15 wt % of at least one isocyanate-reactive            polyol bearing ionic and/or potentially ionic            water-dispersing groups with a weight average molecular            weight ≦500 g/mol;        -   (iv) 0 to 10 wt % of at least one isocyanate-reactive polyol            bearing non-ionic water-dispersing groups;        -   (v) 0 to 15 wt % of at least one isocyanate-reactive polyol            with a weight average molecular weight ≦500 g/mol not            comprised by (iii) or (iv);        -   (vi) 20 to 58 wt % of at least one isocyanate-reactive            polyol not comprised by (iii), (iv) or (v);        -   where (i)+(ii)+(iii)+(iv)+(v)+(vi) add up to 100 wt %;        -   where the NCO/OH ratio is in the range of from 1.2:1 to            2.5:1 to form an isocyanate-terminated prepolymer;    -   II: neutralising the isocyanate-terminated prepolymer with a        neutralising agent;    -   III: forming an aqueous dispersion of the isocyanate-terminated        prepolymer in water;    -   IV: reacting the isocyanate-terminated prepolymer with at least        one active hydrogen chain-extending compound to form the        polyurethane;    -   where the active hydrogen/NCO ratio is in the range of from        0.4:1 to 1.3:1;    -   V: adding vinyl monomer; and    -   VI: polymerising the vinyl monomer added in step V.

The process steps may be carried out in a number of variations.

For example step II may be carried out simultaneously with or beforestep III. Preferably step II is not carried out after step III or stepIV. Preferably step III is not carried out after Step IV. PreferablyStep VI is not carried out before Step III. Step VI is preferablycarried out after Step IV. Step II may be carried out simultaneouslywith step III and the neutralising agent is substantially present in thewater. Preferably Steps II, III and IV are carried out simultaneouslyfollowed by Step V and VI. Steps V may be carried out before and/orduring and/or after Step I, followed by Steps II, III and IV which maybe carried out simultaneously, followed by step VI. Optionally at leasta part of the vinyl monomers added in Step V are added to theisocyanate-terminated prepolymer before step II. Preferably 5 to 30 wt %of vinyl monomer (by weight of isocyanate-terminated prepolymer) areadded before step II. Step II, Step III and/or Step IV may be carriedout by means of one or more in-line mixers. If an in-line mixer is used,preferably at least step II is carried out by means of an in-line mixer.The time between step III and step IV is preferably less than 40minutes, more preferably less than 15 minutes, especially less than 5minutes and most preferably Steps III and IV are carried outsimultaneously. Preferably at least 50 wt % of the active-hydrogen chainextending compound is present in the water before completion of stepIII. Step VI may be carried out by means of a batch polymerisationprocess.

Optionally the isocyanate-terminated prepolymer may be dispersed in apreformed polymer dispersion, including vinyl polymer, polyurethane,alkyd or polyurethane vinyl polymer hybrid dispersions or mixturesthereof.

The aqueous composition of the invention typically has a solids contentof from about 20 to 55% by weight, more usually from 25 to 45% by weightand especially from 29 to 39 wt %.

The aqueous composition of the invention is particularly useful forproviding the principle component of coating compositions (e.g.protective or decorative coating compositions) especially for coatingcomposition for floors for which purpose it may be further diluted withwater and/or organic solvents, or it may be supplied in a moreconcentrated form by evaporation of water and/or organic components ofthe liquid medium. As a coating composition, it may be applied to avariety of substrates including wood (in particular porous wood), board,metals, stone, concrete, glass, cloth, leather, paper plastics, foam andthe like, by any conventional method including brushing, dipping, flowcoating, spraying and the like. The aqueous composition once applied maybe allowed to dry naturally at ambient temperature or the drying processmay be accelerated by the application of heat.

The aqueous composition of the invention may contain conventionalingredients, some of which have been mentioned above; examples includepigments (for example titanium dioxide, iron oxide, chromium basedcompounds and/or metal pthalocyanine compounds), dyes, emulsifiers,surfactants, plasticisers, thickeners, heat stabilisers, matting agentssuch as silica, levelling agents, anti-cratering agents, fillers,sedimentation inhibitors, UV absorbers, antioxidants, drier salts,water-soluble and/or water-insoluble co-solvents, wetting agents,defoamers, fungicides, bacteriocides, waxes and the like introduced atany stage of the production process or subsequently. It is possible toinclude an amount of antimony oxide in the dispersions to enhance thefire retardant properties.

The aqueous composition of the invention preferably contains less than17 wt % of organic co-solvents and more preferably less than 12 wt %based on the weight of the composition. As part of the organicco-solvents an organic co-solvent Q may be added. Organic co-solvent Qcan be added in amounts of 0 to 10 wt %, more preferably 0 to 8 wt % andmost preferably 1 to 5 wt % based on polymer solids. Organic co-solventQ may optionally be added at any stage of the isocyanate-terminatedprepolymer or polyurethane vinyl hybrid preparation to control theviscosity.

Organic co-solvent Q has an evaporation rate from 0.001 to 0.1, morepreferably from 0.002 to 0.05 and most preferably from 0.002 to 0.02,relative to butyl acetate with an evaporation rate of 1.0.

Preferably the organic co-solvent Q is selected from the groupconsisting of oxygen containing co-solvents. Especially preferred areethyldiglycol, butylglycol, butyldiglycol, Dowanol DPnB, and Dowanol DPM(Dowanol is a trade mark of Dow).

If desired the aqueous polyurethane dispersion or polyurethane vinylhybrid dispersion of the invention can be used in combination with otherpolymer compositions which are not according to the invention. Forexample the aqueous polyurethane dispersion may be combined with aprepared vinyl polymer dispersion and then preferably the ratio ofpolyurethane to vinyl polymer is the range of from 95:5 to 30:70, morepreferably 85:15 to 35:65 and most preferably 75:25 to 40:60.

König Hardness as used herein is a standard measure of hardness, being adetermination of how the viscoelastic properties of a film formed fromthe dispersion slows down a swinging motion deforming the surface of thefilm and is measured according to DIN 53157 using an Erichsen hardnessequipment.

Preferably the aqueous composition of the invention when in the form ofa film has a König Hardness ≧70 s, more preferably ≧110 s and mostpreferably ≧150 s.

Elongation at break as used herein is a measure of the elongation atbreak of an unsupported film (i.e. not on a substrate) and is measuredusing an Instron tensile device and is defined as the maximum elongationuntil break under a constant strain rate.

Preferably the aqueous composition of the invention when in the form ofa film has an elongation at break ≧50% and a König Hardness ≧75 s.

The sediment content is determined after preparation of the polyurethanecomposition but before any filtration is carried out.

The aqueous composition of the invention preferably has a sedimentcontent of ≦2.5%, more preferably ≦1%, more preferably ≦0.5% andespecially ≦0.35%.

It is also well known that polyurethanes based substantially on aromaticisocyanates have a tendency to yellow over time. Surprisingly we havefound that polyurethane dispersion of the invention demonstrated asignificant reduction in yellowing when compared to a similar aromaticpolyurethane with high levels of NMP. The yellowness may be determinedby measuring the colour co-ordinates of a film of a composition using aDr Lange Spectro-pen (type LMG161), and ‘b’ is a measure of yellowness(+b) or blueness (−b). The coordinates approach zero for neutral colourssuch as white, grey or black. The higher the values are, the moresaturated a colour is.

The change in yellowness of the resultant film, i.e. the yellowing Δb,was determined by measuring (w) the yellowness of the substrate beforeUV exposure, (x) the yellowness of the film coated in the substratebefore UV exposure, (y) the yellowness of the substrate after UVexposure and (z) the yellowness of the film coated on the substrateafter UV exposure. Yellowing (Δb) is defined as ((z)-(y))-((x)-(w)).

Preferably the value of Δb for the composition of the invention is ≦2.5and more preferably ≦2.1.

In a fifth embodiment of the present invention is provided a method forcoating a substrate with an aqueous composition as described hereincomprising applying the aqueous composition to a substrate.

In a sixth embodiment of the present invention there is provided asubstrate, preferably selected from the group consisting of wood, metal,concrete, plastic and glass, more preferably a floor coated with anaqueous composition as described herein.

The present invention is now illustrated but in no way limited byreference to the following examples. Unless otherwise specified allparts, percentages and ratios are on a weight basis.

Components and abbreviations used:

-   MDI=Isomer mixture of 4,4′-diphenylmethane diisocyanate and    2,4′-diphenylmethane diisocyanate available from Huntsman-   TDI=Toluene diisocyanate, usually as an isomer mixture of    2,4-toluene diisocyanate and 2,6-toluene diisocyanate available from    Huntsman-   Rubinate 9279=Blend of 41 wt % toluene diisocyanate and 59 wt %    diphenylmethane diisocyanate-   IPDI=Isophorone diisocyanate available from Bayer-   NEP=1-ethyl-2-pyrrolidinone available from BASF-   DMPA=Dimethylolpropionic acid available from Perstorp polyols-   CHDM=1,4-Cyclohexanedimethanol available from Eastman Chemical by-   NPG=Neopentyl glycol available from Aldrich MPEG 750=methoxy    polyethylene glycol 750 available from BASF, OH-number=74.9 mgKOH/g-   DEA=Diethanolamine available from Cladic Nederland bv-   PPG1000=Poly propylene glycol 1000, OH-number=110.5 mg KOH/g    available from Dow Benelux-   Terathane 1000=Polytetramethylene ether glycol, OH-number=112.5 mg    KOH/g available from Du Pont de Nemours-   Priplast 3192=Polyester diol, OH-number=56.0 mg KOH/g available from    Uniqema Chemie by-   DMEA=N,N-Dimethylethanolamine available from Chemproha by-   EDA=Ethylene diamine available from Delamine by-   Hydrazine=Hydrazine hydrate available from Bayer AG-   Abex2515=Non-ionic surfactant available from Rhodia-   Disponyl AFX4060=Nonionic surfactant available from Cognis-   Disponyl AFX4030=Nonionic surfactant available from Cognis-   MMA=Methyl methacrylate available from ECEM European Chemical    Marketing by-   STY=Styrene available from Dow Benelux nv-   BMA=n-Butyl methacrylate available from Arkema Nederland by-   n-BA=n-Butyl acrylate available from BASF UK ltd-   2-EHA=2-Ethylhexyl acrylate available from Dow Benelux nv-   IAA Isoascorbic acid available from Brenntag Volkers Benelux by-   tBHPO=tert-Butyl hydroperoxide, available from Akzo Nobel Chemicals    by-   FeEDTA=Iron-ethylenediaminetetracetic acid complex, 1% in water-   Ionol cp=2,6-Di-tert-butyl-4-methylphenol available from Avecia Inc-   NCO=isocyanate group-   UV=ultra violet-   MFFT=minimum film forming temperature

EXAMPLE I Preparation of a Polyurethane Dispersion

A 2000 cm³ flask equipped with a thermometer and overhead stirrer wascharged with Rubinate 9279 (388.1 g). Then a mixture containingTerathane 1000 (230.7 g), CHDM (56.3 g), DMPA (75.0 g) and NEP (250.0 g)was added over a period of 30 minutes. The reaction was allowed toexotherm to 60° C. After the exotherm was complete the reaction was keptat 65° C. for 90 minutes. The NCO content of the resultantisocyanate-terminated prepolymer was 5.27% (theoretical 5.46%).

A dispersion of the resultant isocyanate-terminated prepolymer was madeby feeding 800 g of the isocyanate-terminated prepolymer in 1 hour todeionized water (1554.8 g) containing DMEA (41.9 g), Abex2515 (36.0 g)and 15% hydrazine (100.4 g).

The isocyanate-terminated prepolymer temperature during the dispersionwas kept at 50° C. and the dispersion temperature was controlled between25 to 35° C.

The specifications of the resultant dispersion are listed in Table 1below.

EXAMPLE II Preparation of a Polyurethane Vinyl (50/50) Hybrid Dispersion

To 400 g of the polyurethane dispersion prepared as described in ExampleI was added deionised water (63.5 g), MMA (30.0 g), n-BA (19.0 g) andSTY (51.0 g). After the addition of these monomers the dispersion wasstirred for 1 hour at ambient temperature. To this dispersion was thenadded a 10% tBHPO solution in water (4.0 g) and a 1% FeEDTA solution inwater (1.0 g) followed by feeding a 1% IAA solution in water (40.0 g)over 45 minutes.

The resultant polymer dispersion was filtered through 75 micronfiltercloths and specifications of the resultant dispersion are listedin Table 1 below.

EXAMPLE III Preparation of a Polyurethane Dispersion

A 2000 cm³ flask equipped with a thermometer and overhead stirrer wascharged with Rubinate 9279 (347.6 g). Then a mixture containingTerathane1000 (297.4 g), CHDM (45.0 g), DMPA (60.0 g) and NEP (250.0)was added over a period of 45 minutes. The reaction was allowed toexotherm to 65° C. After the exotherm was complete the reaction was keptat 65° C. for 90 minutes. The NCO content of the resultantisocyanate-terminated prepolymer was 4.75% (theoretical 4.89%).

A dispersion of the resultant isocyanate-terminated prepolymer was madeby feeding 800 g of the isocyanate-terminated prepolymer in 1 hour todeionised water (1567.6 g) containing DMEA (33.5 g), Abex2515 (36.0) and15.2% hydrazine (90.5 g).

The isocyanate-terminated prepolymer temperature during the dispersionwas kept at 50° C. and the dispersion temperature was controlled between25 to 35° C.

The specifications of the resultant dispersion are listed in Table 1below.

EXAMPLE IV Preparation of a Polyurethane Vinyl (50/50) Hybrid Dispersion

To 400 g of the polyurethane dispersion prepared as described in ExampleI was added deionised water (63.5 g), MMA (30.0 g), nBA (19.0 g) and STY(51.0 g). After the addition of these monomers the dispersion wasstirred for 1 hour at ambient temperature. To this dispersion was thenadded a 10% tBHPO solution in water (4.0 g) and a 1% FeEDTA solution inwater (1.0 g) followed by feeding a 1% IAA solution in water (40.0 g)over 45 minutes.

The resultant polymer dispersion was filtered through 75 micronfiltercloths. The specifications of the resultant dispersion are listedin Table 1 below.

EXAMPLE V Preparation of a Polyurethane Vinyl (43/57) Hybrid

Stage 1

To 1459.5 g of MPEG 750 (M_(w)=740 g/mole), 2,4-TDI (343.8 g) was addedover a 90 minute period at 40-45° C. At the end of the reaction, theisocyanate content was 4.60%. The system was cooled to 25° C. and DEA(196.7 g) was added. The nonionic diol had an OH number of 103 mg KOH/g.

Stage 2

A 2000 cm³ flask equipped with a thermometer and overhead stirrer wascharged with Rubinate 9279 (361.2 g) and IPDI (90.3 g). Then a mixturecontaining Terathane1000 (476.7 g), CHDM (55.3 g), DMPA (66.3 g),non-ionic diol from stage 1 (55.3 g) and NEP (368.3 g) was added over aperiod of 45 minutes. The reaction was allowed to exotherm to 70° C.After the exotherm was complete the reaction was kept at 65° C. for 90minutes. The NCO content of the resultant isocyanate-terminatedprepolymer was 3.67% (theoretical 4.01%).

A dispersion of the resultant isocyanate-terminated prepolymer was madeby feeding 250 g of the isocyanate-terminated prepolymer in 1 hour todeionised water (914.9 g) containing MMA (150.0 g), BMA (100.0 g), DMEA(6.9 g), Disponyl AFX4030 (18.8) and 15.2% hydrazine (20.7 g). Afterdispersing a 10% tBHPO solution in water (6.5 g) and a 1% FeEDTAsolution in water (3.3 g) was added followed by feeding a 2.5% IAAsolution in water (20.0 g) over 45 minutes.

The isocyanate-terminated prepolymer temperature during the dispersionwas kept at 50° C. and the dispersion temperature was controlled between25 to 35° C. The specifications of the resultant dispersion are listedin Table 1 below.

EXAMPLE VI Preparation of a Polyurethane Dispersion

A dispersion of the isocyanate-terminated prepolymer described inexample V was made by feeding 600.0 g of the isocyanate-terminatedprepolymer in 1 hour to deionised water (857.6 g) containing DMEA (16.4g), Disponyl AFX 4030 (45.0) and 15.2% hydrazine (49.7 g).

The isocyanate-terminated prepolymer temperature during the dispersionwas kept at 50° C. and the dispersion temperature was controlled between25 to 35° C. The specifications of the resultant dispersion are listedin Table 1 below.

EXAMPLE VII Preparation of a Polyurethane Vinyl (50/50) HybridDispersion

To 300.0 g of the polyurethane dispersion prepared as described inExample VI was added deionised water (146.0 g), MMA (60.0 g) and BMA(30.0 g). After the addition of these monomers the dispersion wasstirred for 1 hour at ambient temperature. To this dispersion was thenadded a 10% tBHPO solution in water (2.3 g) and a 1% FeEDTA solution inwater (1.2 g) followed by feeding a 2.5% IAA solution in water (7.2 g)over 45 minutes.

The resultant polymer dispersion was filtered through 75 micronfiltercloths. The specifications of the resultant dispersion are listedin Table 1 below.

EXAMPLE VIII Preparation of a Polyurethane Dispersion

A 2000 cm³ flask equipped with a thermometer and overhead stirrer wascharged with TDI (421.3 g). Then a mixture containing Priplast 3192(518.0 g), NPG (55.3 g), DMPA (110.5 g) and NEP (368.3) was added over aperiod of 45 minutes. The reaction was allowed to exotherm to 65° C.After the exotherm was complete the reaction was kept at 65° C. for 90minutes. The NCO content of the resultant isocyanate-terminatedprepolymer was 4.44% (theoretical 4.60%).

A dispersion of the resultant isocyanate-terminated prepolymer was madeby feeding 60 g of the isocyanate-terminated prepolymer in 1 hour todeionised water (862.0 g) containing DMEA (32.9 g), Disponyl AFX4060(22.5) and 15% hydrazine (54.8 g).

The isocyanate-terminated prepolymer temperature during the dispersionwas kept at 50° C. and the dispersion temperature was controlled between25 to 35° C. The specifications of the resultant dispersion are listedin Table 1 below.

EXAMPLE IX Preparation of a Polyurethane Vinyl (70/30) Hybrid Dispersion

To 400.0 g of the polyurethane dispersion prepared as described inExample VIII was added deionised water (63.8 g), MMA (32.0 g) and STY(20.0 g). After the addition of these monomers the dispersion wasstirred for 1 hour at ambient temperature. To this dispersion was thenadded a 10% tBHPO solution in water (1.4 g) and a 1% FeEDTA solution inwater (0.7 g) followed by feeding a 2.5% IAA solution in water (4.2 g)over 45 minutes.

The resultant polymer dispersion was filtered through 75 micronfiltercloths. The specifications of the resultant dispersion are listedin Table 1 below.

EXAMPLE X Preparation of a Polyurethane Vinyl (45/55) Hybrid Dispersion

To 240.0 g of the polyurethane dispersion prepared as described inExample VIII was added deionised water (188.4 g), MMA (72.0 g) and n-BA(16.0 g). After the addition of these monomers the dispersion wasstirred for 1 hour at ambient temperature. To this dispersion was thenadded a 10% tBHPO solution in water (2.3 g) and a 1% FeEDTA solution inwater (1.1 g) followed by feeding a 2.5% IAA solution in water (7.0 g)over 45 minutes.

The resultant polymer dispersion was filtered through 75 micronfiltercloths. The specifications of the resultant dispersion are listedin Table 1 below.

Sediment Determination

Sediment is unstabilised solid material (in the order of microns ratherthan nanometers) which is formed during dispersing or reaction and whichwill settle or precipitate upon storage and/or heating. It may bedetermined quantitatively by centrifuging. The sediment content wasdetermined by taking 50 cm³ of the resultant dispersion of the examplesprepared above, diluting this with water (1:1) and centrifuging thediluted composition for 15 minutes at 1500 rpm (276G) rpm in acentrifuge tube.

Each division on the tube tip represents 0.05 cm³ or 0.05% sediment. Theoutcome, i.e. the level of solid sediment in the tube tip was thenmultiplied by 2 to take into account the dilution factor.

TABLE 1 Example I II III IV V Solids [%] 25.6 34.1 25.5 33.6 29.8 pH 7.98.3 7.9 8.3 7.4 Viscosity [mPa · s] * 50 156 50 121 50 Sediment [%] #0.3 0.4 0.3 0.3 0.2 Absorbance ** <5 30 <5 74 100 Particle size [nm] 24131 28 142 64 MFFT [° C.] <5 <5 <5 <5 <5 KH [s] *** 193 209 158 195 153Elongation at 163 125 197 184 134 break [%] Yellowness ## 1.2/3.10.4/2.3 1.6/3.4 0.6/2.5 0.0/2.0 Yellowing Δb 0.9 1.9 1.8 1.9 2.0 ExampleVI VII VIII IX X Solids [%] 28.8 27.5 30.5 42.2 33.5 pH 7.5 7.6 7.5 8.48.0 Viscosity [mPa · s] * 500 840 250 11360 1460 Sediment [%] # 0.2<0.05 0.2 0.10 0.15 Absorbance ** <5 5 14 28 74 Particle size [nm] 57 46142 264 268 MFFT [° C.] <5 <5 <5 <5 <5 KH [s] *** 75 167 115 171 166Elongation at 236 175 215 107 58 break [%] Yellowness ## 0.2/2.0 0.1/1.90.4/2.3 0.2/1.8 0.5/2.4 Yellowing Δb 1.8 1.8 1.9 1.6 1.9 * A Brookfieldviscosity at 25° C. ** The measured absorbance by spectrometry at 650 nmusing a path length of 1 mm. *** The König Hardness (KH) of a dried filmcast on a glass plate with a wet film thickness of 80 micron. # Thesediment was determined before filtration. ## The yellowness of thedried film before UV exposure/after UV exposure where the UV exposurewas 10 × 400 mJ/cm².

1. An aqueous composition with a sediment content ≦5%, comprising apolyurethane dispersion and containing ≦5 wt % of1-methyl-2-pyrrolidinone by weight of the polyurethane, wherein thepolyurethane has an acid value in the range of from 24 to 65 mgKOH/g andis obtained by the reaction of: A) an isocyanate-terminated prepolymerformed from components comprising: (i) 30 to 60 wt % of at least onearomatic organic polyisocyanate; (ii) 0 to 30 wt % of at least onealiphatic organic polyisocyanate; (iii) 0 to 15 wt % of at least oneisocyanate-reactive polyol bearing ionic and/or potentially ionicwater-dispersing groups with a weight average molecular weight ≦500g/mol; (iv) 0 to 10 wt % of at least one isocyanate-reactive polyolbearing non-ionic water-dispersing groups; (v) 0 to 15 wt % of at leastone isocyanate-reactive polyol with a weight average molecular weight≦500 g/mol not comprised by (iii) or (iv); (vi) 20 to 58 wt % of atleast one isocyanate-reactive polyol not comprised by (iii), (iv) or(v); where (i)+(ii)+(iii)+(iv)+(v)+(vi) add up to 100 wt %; where theNCO/OH ratio is in the range of from 1.2:1 to 2.5:1; and B) at least oneactive-hydrogen chain extending compound; where the active-hydrogen/NCOratio is in the range of from 0.4:1 to 1.3:1; in the presence of (a) ≦5wt % of 1-methyl-2-pyrrolidinone by weight of polyurethane, (b) 5 to 100wt % of 1-ethyl-2-pyrrolidinone by weight of polyurethane and (c) water.2. An aqueous composition according to claim 1 wherein at least 20 to 80wt % of component (i) consists of methylenebis(phenyl isocyanate).
 3. Anaqueous composition according to claim 1 where components(i)+(ii)+(iii)+(V) add up to ≧42 wt %.
 4. An aqueous compositionaccording to claim 1 wherein the ionic water-dispersing groups in theisocyanate-terminated prepolymer are neutralised with a neutralisingagent in the range of from 0.5:1 to 1.4:1.
 5. An aqueous compositionaccording to claim 1 wherein ≧60 wt % of the carboxylic acid groups inthe isocyanate-terminated prepolymer are neutralised with an oxygencontaining amine.
 6. An aqueous composition according to claim 5 wherethe oxygen containing amine is selected from the group consisting ofN-ethyl morpholine; N-methyl morpholine; and R¹(R²)NR³OH with a Mn inthe range of from 88 to 118, where R₁, R₂ and R₃ are independently C₁ toC₄ alkyl.
 7. An aqueous composition according to claim 1 which when inthe form of film has a König Hardness ≧75 s.
 8. An aqueous compositionaccording to claim 1 which when in the form of a film has an elongationat break ≧50% and a König Hardness ≧75 s.
 9. An aqueous compositionaccording to claim 1 with a solids content in the range of from 20 to 55wt %.
 10. An aqueous composition according to claim 1 with a weightaverage particle size less than 500 nm.
 11. An aqueous compositionaccording to claim 1, wherein all of the isocyanate groups are directlybonded to an aromatic group, irrespective of whether aliphatic groupsare also present.
 12. A substrate having a coating obtainable from anaqueous composition according to claim
 1. 13. A substrate according toclaim 12 selected from the group consisting of wood, metal, concrete,plastic and glass.
 14. A floor having a coating obtained from an aqueouscomposition according to claim
 1. 15. A process for making an aqueouscomposition with a sediment content ≦5%, comprising a polyurethanedispersion and containing ≦5 wt % of 1-methyl-2-pyrrolidinone by weightof the polyurethane, wherein the polyurethane has an acid value in therange of from 24 to 65 mgKOH/g and where the process is carried out insteps comprising: I: reacting in the presence of (a) ≦5 wt % of1-methyl-2-pyrrolidinone by weight of polyurethane and (b) 5 to 100 wt %of 1-ethyl-2-pyrrolidinone by weight of polyurethane: (i) 30 to 60 wt %of at least one aromatic polyisocyanate; (ii) 0 to 30 wt % of at leastone aliphatic polyisocyanate; (iii) 0 to 15 wt % of at least oneisocyanate-reactive polyol bearing ionic and/or potentially ionicwater-dispersing groups with a weight average molecular weight ≦500g/mol; (iv) 0 to 10 wt % of at least one isocyanate-reactive polyolbearing non-ionic water-dispersing groups; (v) 0 to 15 wt % of at leastone isocyanate-reactive polyol with a weight average molecular weight≦500 g/mol not comprised by (iii) or (iv); (vi) 20 to 58 wt % of atleast one isocyanate-reactive polyol not comprised by (iii), (iv) or(v); where (i)+(ii)+(iii)+(iv)+(v)+(vi) add up to 100 wt %; where theNCO/OH ratio is in the range of from 1.2:1 to 2.5:1 to form anisocyanate-terminated prepolymer; II: neutralising theisocyanate-terminated prepolymer with a neutralising agent; III: formingan aqueous dispersion of the isocyanate-terminated prepolymer in water;and IV: reacting the isocyanate-terminated prepolymer with at least oneactive hydrogen chain-extending compound to form the polyurethane; wherethe active hydrogen/NCO ratio is in the range of from 0.4:1 to 1:3:1.16. A process according to claim 15 where step II is carried out bymeans of at least an in-line mixer.
 17. A process according to claim 15where the time between step III and step IV is less than 40 minutes. 18.A method of coating a substrate using an aqueous composition accordingto claim 1 comprising applying the aqueous composition to a substrate.